Locomotives operated at high altitudes and in the far northern and southern regions of the globe are subject to severe environmental conditions which may have an adverse affect on the locomotive, including low atmospheric pressure, cold temperatures, and blowing and drifting snow.
One problem involves blockage of the filters and/or ducts. It is known that snow may be drawn into the air inlet ducts of a locomotive and may accumulate in sufficient quantities to obstruct the passage of air through the ducts. Thus, it is not uncommon for snow to accumulate on air filters disposed in the air inlet pathway of the locomotive. Such accumulations of snow may act to reduce the power output of the engine and/or may cause the engine to cease from operating completely. One way to solve this problem involves providing summer/winter doors which function to connect the air inlet duct with a source of warm air so that the cold ambient air is mixed with relatively warmer air prior to passing through the final air filters. In this case, these doors allow if the temperature of the inlet air mixture can be maintained above the freezing point, any snow /or ice that may develop or be deposited on the filters and/or ductwork will melt rather than accumulating and restricting the intake airflow. When warm air is needed to prevent the buildup of snow/ice, the summer/winter doors are opened making warm air from the engine compartment available allowing the radiant and convection heat from the engine to warm the air near the filters and/or ductwork.
Another problem involves the control of cylinder pressure to prevent the de-rating of the Gross Horse Power (GHP) on cold days. This is because relatively large compression-ignition engines, such as those used for locomotives, are usually operated at a full load with peak cylinder pressure (Pp), close to but not exceeding a maximum structurally allowable cylinder pressure value (Pmax). As the ambient temperature drops below a nominal operating temperature (assuming ambient pressure (Pa) remaining unchanged), the peak cylinder pressure increases and may exceed the maximum structurally allowable cylinder pressure value. This is undesirable because it increases the engine component stress and loading.
Another problem involves the surge margin (or engine stability limit) under cold ambient conditions and a high Manifold Air Temperature (MAT). Under these conditions the engine operating point as plotted on a turbocharger compressor performance map, moves toward an area of unstable operation called the surge line. This is often made worse at high altitudes.